You can perform factory data reset to return your phone to its factory defaults settings. This setting erases all data from your phone, including your Google or other email account settings, system and application data and settings, and downloaded applications. It will not erase current system software and bundled applications, or files stored on an optional installed memory card, such as music or photos. To reset Samsung Mesmerize Galaxy S SCH I500:

From the Home screen, touch Menu ➔ Settings ➔ Privacy.

Touch Factory data reset, then follow the prompts to perform the reset.